The present invention relates generally to making metal sheet in a manner that reduces the amount or degree of earing encountered when cans are made from the sheet.
The rims of drawn and ironed (D&I) cans often exhibit a number of high areas called ears and a number of intervening low areas called troughs. The ears are wavy symmetrical projections formed in the course of deep drawing or spinning as a result of directional properties or anisotropy in sheet. Ears occur in groups of 4 or 8 with the peaks of the projections located at 45 degrees and/or at 0 and 90 degrees to the rolling direction. Degree of earing is the difference between average height at the peaks and average height at the valleys, divided by average height of cup or can, multiplied by 100 and expressed in percent. The ears and troughs are a problem in that can making machinery requires an even, level rim, i.e., a small ear to trough height difference relative to average can height, in order to prevent jamming of the machinery and tearing of the cans. If a trimming operation is performed, the ear metal can generate a substantial amount of scrap metal, and a cost factor for each can trimmed. Hence, high earing, i.e., in excess of three percent, relative to mean cup height, is a problem that needs to be overcome and should be reduced as much as possible.